The primary hypothesis is that systemic markers of oxidative stress and lipid peroxidation, as measured by F2-isoprostanes, will be significantly lower in patients with severe sepsis and detectable cell-free hemoglobin who receive acetaminophen compared to placebo. The secondary hypothesis is that patients with severe sepsis and detectable cell-free hemoglobin treated with acetaminophen will have better clinical outcomes, including decreased incidence of acute kidney injury and lower rates of hospital mortality, compared to those who receive placebo.